An alkane can be converted to the corresponding alkene by several processes, including partial oxidation and thermal cracking. According to these processes, for example, propane may be converted to propylene. Other alkanes can also be similarly converted to a corresponding alkene, for example: butane to one or more of 1-butene and 2-butene, and ethyl benzene to styrene.
Propane can be chemically oxidized to a mixture of products including propylene by reaction with a limited amount of oxygen. Catalysts are known for the activation of propane. When a mixture of propane and a limited amount of oxygen is passed over a catalyst a mixture of products is formed, including propylene, other hydrocarbon products, and oxides of carbon. It is very difficult to oxidize propane selectively to propylene. Typically, when propane is heated to a high temperature, typically several hundreds of degrees Celsius, the propane is cracked to form a mixture containing hydrogen, propylene, ethane, methane, ethylene, and higher hydrocarbons. The cracking process consumes energy. Further, the cracking process is not highly selective to propylene, and typically operates at low conversion. It is therefore necessary to separate the products of a catalytic oxidation reaction to obtain propylene in a commercially saleable or useable form (e.g., with other reaction products of the cracking process removed of reduced on a volume percent). Further, the heat generated by the oxidation reaction is recoverable only as process energy and not as high-grade energy such as electricity.
When a fuel is oxidized in a fuel cell, the products are the oxidation products from the fuel and electrical energy. Oxide ion conducting solid membranes are used in solid oxide fuel cells (a “SOFC”). In such cells, a source of oxygen is fed to a cathode catalyst where the oxygen combines with electrons to form oxide ions. The oxide ions pass through the solid membrane from the cathode to the anode. At a catalytic anode in a SOFC, oxide ions react with a fuel to generate oxidation products and electrons. When the fuel is propane, the oxidation products are usually oxides of carbon. Thus an oxide ion conducting SOFC can be designed to use propane as fuel. Mazanec et al. in U.S. Pat. No. 4,933,054 which issued in 1990, describe an electrochemical process using oxide ion conducting SOFC at temperatures in the range of about 500° C. to about 950° C. for electrochemical oxidative dehydrogenation of saturated hydrocarbons. The saturated hydrocarbons have from 2 to 6 carbon atoms, and include propane, and are converted to the corresponding unsaturated hydrocarbons, including propylene. Michaels and Vayenas, in Journal of Catalysis, Volume 85, 477-487 (1984), describe electrochemical oxidative dehydrogenation of ethyl benzene to styrene in the vapor phase using SOFC operated at high temperatures (e.g. above 650° Celcius).
Proton conducting solids are known, including polymer electrolyte membranes (“PEM”). PEM are used in H2—O2 fuel cells, an example of which is as described by Fuglevand et al. in U.S. Pat. No. 6,030,718. The hydrogen used as fuel in PEM fuel cells can be generated in several ways. Propane can be reformed to generate a hydrogen containing fuel for a fuel cell, and can be used as a coolant for a fuel cell. For example, Ziaka and Vasileiadis in U.S. Pat. No. 6,090,312, issued in 2000, disclose reforming reactions of light hydrocarbons having from 1 to 4 carbon atoms to generate hydrogen for use as fuel in a fuel cell. Nakagaki et al. in U.S. Pat. No. 6,099,983, issued in 2000, discloses reforming of propane to generate a hydrogen containing gas that is used as fuel in a fuel cell, in which the reformed hydrogen containing gas also serves as coolant for the fuel cell. Each of the above examples uses propane as a source of hydrogen to be used as fuel, and does not use propane as fuel.